1. Field of the Invention
The invention relates to an engine start control apparatus and engine start control method that start an internal combustion engine in such a manner that an electric rotating machine is driven for cranking a crankshaft of the internal combustion engine, and also relates to a vehicle equipped with the engine start control apparatus.
2. Description of the Related Art
Generally, an internal combustion engine (engine) is started in such a manner that a crankshaft of the engine is driven for rotation by an electric rotating machine (motor) (hereinafter, referred to as “cranking”). In addition, there is a case where the engine is provided with a variable valve timing mechanism that is able to vary the timing at which the intake valve and/or exhaust valve of the engine are opened or closed.
There is a technique that, in a vehicle equipped with the engine having a variable valve timing mechanism, the intake valve is controlled so as to close at a timing that is delayed from the bottom dead center during cranking, that is, the closing timing of the intake valve is retarded, to decrease the actual compression ratio and, as a result, vibrations that occur in the vehicle during starting of the engine are reduced. In the vehicle in which the closing timing of the intake valve is set to a predetermined retarded position during cranking, when the engine is started at a low temperature, there is a case that, in order to improve startability of the engine by increasing the actual compression ratio, the closing timing of the intake valve is controlled to advance from the predetermined retarded position toward the bottom dead center. In this case, the amount of advance (advance amount) of the closing timing of the intake valve is, for example, determined on the basis of the temperature of an engine coolant. For example, as the coolant temperature decreases, the advance amount of the closing timing of the intake valve is increased.
Japanese Patent Application Publication No. 2007-85253 (JP-A-2007-85253) describes a technique that, in an engine having a hydraulic variable intake valve timing mechanism, the engine is started by cranking. In the technique described in JP-A-2007-85253, the variable intake valve timing mechanism is actuated by hydraulic pressure of the oil that is supplied by a pump being driven by rotational force of the crankshaft of the engine. In the technique described in JP-A-2007-85253, the hydraulic pressure of the oil that is supplied by the pump is detected, and electric power supplied to a motor for cranking is controlled on the basis of a delay from the time at which cranking is started until the variable intake valve timing mechanism actually starts advancing the closing timing of the intake valve by an increase in hydraulic pressure.
Incidentally, if an abnormality occurs in the variable valve timing mechanism, even when the advance of the closing timing of the intake valve is instructed during cranking, the instructed amount of advance is not actually achieved. When the closing timing of the intake valve is not actually advanced during cranking despite an advance instruction of the closing timing of the intake valve, it is difficult to ensure a necessary amount of intake air for starting the engine and, therefore, startability of the engine deteriorates in comparison with the case in which the instructed amount of advance is achieved.